COMPARATIVE-ASSESSMENT OF BACTERIAL INOCULATION AND PROPIONIC-ACID TREATMENT ON AEROBIC STABILITY AND MICROBIAL-POPULATIONS OF ENSILED HIGH-MOISTURE EAR CORN

High-moisture ear corn (HMEC) was untreated, treated with propionic ac id (PA), or inoculated with a mixture of Lactobacillus plantarum and E nterococcus faecium and allowed to ensile in laboratory silos for 0, 7 , 21, 42, 138, or 202 d. The silages were evaluated for fermentation q uality, microbial populations, and aerobic stability. In all treatment s, silage pH declined rapidly within 7 d, but the rate of decline seem ed greatest with the inoculum. The lactic acid content of inoculated H MEC was higher (P < .05) than that of control or PA-treated HMEC. Rega rdless of treatment, the population of lactic acid bacteria (LAB) incr eased (P < .1) up to 7 to 21 d of fermentation then declined; LAB coun ts decreased (P < .05) up to 42 d in control and PA-treated silage but continued to decline until 138 d for inoculated silage. Yeast and mol d counts tended to decrease up to 42 d of ensiling then increased (P < .05) as fermentation progressed. Between 138 and 202 d of ensiling, t he control silage showed a marked increase (P < .10) in pH and yeast a nd mold populations, providing evidence of secondary fermentation; PA treatment and bacterial inoculation prevented secondary fermentation. Inoculation tended to reduce estimates of sample temperature for silag e stored for 138 d and exposed to air, but not for the corresponding s ilage stored for 202 d. Treatment with PA prevented the loss (P > .05) of acetic acid and the rise (P > .05) in pH during air exposure of th e 138-d silage; both control and PA-treated silage showed an increase (P < .05) in yeast and mold populations, but the increments were 38% a nd 23%, respectively. Compared with PA, the relative efficacy of inocu lation in improving aerobic spoilage of HMEC depended on the period of silo storage and the criterion used to assess aerobic stability.